import java.util.*;

public class Main {
    private static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) throws Exception {
        int n = sc.nextInt();
        List<Integer> list = new ArrayList<>();
        for (int i=0;i<n;i++) {
            list.add(sc.nextInt());
        }
        
        Collections.sort(list);
        
        int diff = list.get(1) - list.get(0);
        
        for (int i=1;i<n-1;i++) {
            int tmp = list.get(i+1) - list.get(i);
            if (tmp != diff || tmp == 0) {
                System.out.println("NO");
                return;
            }
        }
        
        System.out.println("YES");
    }
}